Methods and systems for detecting entities in a biological sample

ABSTRACT

Apparatus and methods for use with a blood sample are described. The blood sample is stained with Hoechst stain and Acridine Orange stain. A plurality of images of the blood sample are acquired. An object is identified as being a white blood cell candidate. A first stained area, which is stained by the Hoechst stain and which is disposed within the white blood cell candidate, is identified. A second stained area, which is stained by the Acridine Orange stain and which is disposed within the white blood cell candidate, is identified. A white blood cell is detected by determining that structural features of the stained areas satisfy predetermined criteria associated with a white blood cell. Other applications are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/369,251 to Pollak (published as US 2015/0037806), which is a US national phase application of PCT Application No. PCT/1112012/050556 to Pollak (published as WO 13/098821), filed Dec. 27, 2012, which claims the benefit of:

PCT Application No. PCT/2011/000973 to Bachelet (published as WO 12/090198), filed Dec. 29, 2011; and

U.S. Provisional Application No. 61/664,769 to Pollak, filed Jun. 27, 2012.

TECHNOLOGICAL FIELD

The present disclosure concerns diagnostic methods and in particular, methods and systems for detecting pathogens in bodily fluids.

PRIOR ART

References considered to be relevant as background to the presently disclosed subject matter are listed below:

-   J. Keiser, J. Utzinger, I. Premji Y. Yamagata and B. H. Singer in     Annals of Tropical Medicine & Parasitology, Vol. 96, No. 7, 643-654     (2002) -   U.S. Pat. No. 5,470,751 -   On line publication of Centers for Disease Control and Prevention     CDC, Diagnostic Procedures, 2009 “Blood specimens: Microscopic     Examination” at     http://www.dpd.cdc.gov/dpdx/HTML/Frames/DiagnosticProcedures/body_dp_bloodexamin.htm

Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

BACKGROUND

Staining is a technique frequently used in biology and medicine to highlight structures in biological tissues for viewing, often with the aid of different microscopes. Stains may be used to define and examine bulk tissues (highlighting, for example, muscle fibers or connective tissue), cell populations (classifying different blood cells, for instance), or organelles within individual cells.

Cell staining is used to better visualize cells and cell components under a microscope. By using different stains, one can preferentially stain certain cell components, such as a nucleus or a cell wall, or the entire cell. The stains can be used on fixed, or non-living cells, as well as on living cells.

Cell staining techniques are also often used to detect a pathogen in a blood sample. One important pathogen is the malaria.

The first dye synthesized for detection by staining methylene blue, in 1876. Six years later, it was used to discover tubercle bacillus. Within the years, modifications of MB were employed, including, “ripened” MB in combination with other dyes, such as eosin, which allowed differentiation between blood cells and the nuclei of malarial parasites, as well as the combination of MB methylene blue demethylation with glycerol as a stabilizing agent in methanol solvent, known as the Malachowski-Wright-Giemsa stain.

J. Keiser et al. describe Acridine Orange in comparison to Giemsa stain, for malaria diagnosis, including its diagnostic performance, its promotion and implementation and the implications for malaria control.

U.S. Pat. No. 5,470,751 describes another reagent for staining malaria infected cells and a method for detecting malaria infected cells using the same, wherein the reagent is a staining solution comprising at least one first dye of an Auramine analogue, such as Auramine O and at least one second dye of a condensed benzene derivative, such as 3,3′-diethyl-2,2′-oxacarbocyanine iodide. A test sample is treated with reagent to stain malaria infected cells. The stained malaria infected cells are then optically detected.

In addition, the Centers for Disease Control and Prevention CDC, Diagnostic Procedures, 2009 describes under the heading “Blood specimens: Microscopic Examination” the Kawamoto technique for the detection of blood parasites, such as malaria parasites, using fluorescent dyes that stain nucleic acids. As discussed in this publication, in the Kawamoto technique, blood smears on a slide are stained with acridine orange (AO) and examined with either a fluorescence microscope or a light microscope adapted with an interference filter system. This results in a differential staining of nuclear DNA in green and of cytoplasmic RNA in red, which allows recognition of the parasites.

GENERAL DESCRIPTION

The present disclosure provides, in accordance with a first of its aspects, a method of detecting a pathogen infection in a sample, the method comprising:

-   -   staining said bodily sample with two or more dyes, comprising at         least one dye predominantly staining DNA to thereby provide         differential staining between DNA and at least one other         cellular component being different from DNA;     -   identifying at least a first stained area comprising the DNA, if         exists in the sample, and at least one other stained area         comprising the other cellular component;     -   extracting structural features for the first stained area and         the at least one other stained area, said structural features         comprise at least one of (i) size of at least one of the first         stained area and one other stained area and (ii) location of         said first stained area and said at least one other stained area         one with respect to the other; and     -   determining the presence of a suspected pathogen in the sample         if a first stained area was identified and said structural         features conform to structural features predetermined as         characterizing the suspected pathogen.

In accordance with a second aspect, the present disclosure provides a kit comprising:

-   -   a first dye predominantly staining DNA;     -   a second dye for staining at least one other cellular component         being different from DNA;     -   instructions for use of said first dye and said second dye in         determining presence of a suspected pathogen in a sample,

In accordance with a third aspect, the present disclosure provides a system comprising:

-   -   an image capturing component configured and operable to acquire         at least one optical image of a stained area in a sample, the         stained area comprising a first stained area corresponding         predominantly to DNA and at least one other stained area         corresponding to at least one other cellular component being         different from DNA;     -   an image processing unit configured to     -   i) extract structural features of said at least first stained         area and said one other stained area, said structural features         comprise at least one of (i) size of at least one of said first         stained area, and (ii) one other stained area; and a location of         said first stained area and said one other stained area one with         respect to the other; and     -   ii) determine the presence of a suspected pathogen in the bodily         sample, if a first stained area is identified and said         structural features conform to structural features predetermined         as characterizing a pathogen infection,

Yet, in accordance with a fourth aspect, the present disclosure provides a processing unit for identifying a pathogen in a sample, comprising:

-   -   input module configured and operable to receive data         corresponding to a stained object in the sample comprising at         least a first stained area corresponding predominantly to DNA         and at least one other stained area corresponding to at least         one other cellular component being different from DNA, and     -   an image processing unit configured and operable to process said         data corresponding to said stained object, the processing         comprises:     -   extracting structural features for the at least the first         stained area and second stain area in the stained object, said         structural features comprise at least one of (i) area of at         least one of the first and the one other stained area and (ii) a         location of said first stained area and said one other stained         area one with respect to the other; and     -   providing a value or combination of values being indicative of         the presence or absence of a suspected pathogen in the sample,         if said structural features conform to structural features         predetermined as characterizing the suspected pathogen

In accordance with a fifth aspect, the present disclosure provides a computer program product comprising a computer useable medium having computer readable program code embodied therein for detecting a pathogen infection in a sample being stained with two or more dyes, the computer program product comprising:

computer readable program code for causing the computer to identify in the stained object at least a first stained area corresponding predominantly to DNA and at least one other stained area corresponding to at least one other cellular component being different from DNA;

computer readable program code for causing the computer to extract structural features for the at least a first stained area and one other stain area, said structural features comprise at least one of (i) area of at least one of the first and one other stained areas and (ii) location of said first stained area and said one other stained area one with respect to the other;

computer readable program code for causing the computer to determine a value or combination of values being indicative of the presence of a suspected pathogen in the sample if said structural features conform to structural features predetermined as characterizing the suspected pathogen infection.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIGS. 1A-1F show images obtained at three different exposures; the bright field (FIGS. 1A, 1D), blue fluorescence (365 nm, FIGS. 1B and 1E) and UV fluorescence (475 nm, FIGS. 1C, 1F) images of white blood cells (FIGS. 1A-1C) and malaria infected red blood cells (FIGS. 1D-IF).

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention is based on the development of methods for differential stain different components in a blood sample to thereby allow an almost instant detection of an infection in the blood.

Specifically, it has been found by the inventors that staining of a blood sample with acridine orange (AO) reagent allows differentiation between DNA containing pathogens and, for example, platelets, reticulocytes, Howell-Jolly bodies, and bacteria such as Staphylococcus epidermidis.

It has been further found that staining of a blood sample with AO and Hoechst reagents and by employing an image analysis of the stained object including the two different stained areas (the object being an image in the field of view comprising the stained areas under examination), allowed detection of malaria infection in the blood sample. In this connection, the inventors have found that in addition to detecting two different stained areas in the viewed stained object (of the sample), it is sometimes also important to take into consideration some spatial features of the stained areas, such as the size or dimensions of each stained area and/or the spatial relationship therebetween.

The inventors have also determined that in order to detect a pathogen in the blood sample, at least one dye should stain deoxyribonucleic nucleic acid (DNA) with preference over staining of other cellular components.

It has been further found by the inventors that the diagnostic sensitivity obtained by using two dyes, one predominantly staining DNA, is above 95%, and even above 97% or 99%.

Further, it has been found, and was also shown in the following example, that the method disclosed herein allows identifying the presence of a pathogen at low counts/O. For example, the example provided herein shows that a parasite, such as Plasmodium may be detected in the blood even at a count below 1,000 parasites per μl and even at a low count of about 20 parasites per μl.

Thus, in accordance with a first aspect, the present disclosure provides a method of detecting a pathogen infection in a sample, the method comprising:

-   -   staining said bodily sample with two or more dyes, with at least         one dye predominantly staining DNA to thereby provide         differential staining between DNA and at least one other         cellular component, being different from DNA;     -   identifying at least a first stained area comprising the DNA, if         exists in the sample and at least one other stained area         comprising the other cellular component;     -   extracting spatial features for the first stained area and the         at least one other stained area, said spatial features comprise         at least one of: (i) size of at least one of the first stained         area and one other stained area; and (ii) location of the first         stained area and the at least one other stained area one with         respect to the other;     -   determining the presence of a pathogen in the sample if a first         stained area was identified and said spatial features conform to         (namely, matches, corresponds to, falls within, is associated         with), a value or a combination of values predetermined as         characterizing a suspected pathogen infection.

As appreciated, while the invention is described in the following detailed description with reference to a method of detecting a pathogen infection in a sample, such as a blood sample, it is to be understood that the present disclosure also encompass a kit for performing the invention, a system, a processing unit and other aspects, as disclosed herein,

The method of the invention is applicable for a variety of samples. In some embodiments, the sample is a bodily sample. In some embodiments, the bodily sample is a fluid bodily sample such as, without being limited thereto, blood, saliva, semen, sweat, sputum, vaginal fluid, stool, breast milk, bronchoalveolar lavage, gastric lavage, tears and nasal discharge.

In some embodiments, the bodily sample is a blood sample.

In some embodiments, the blood sample is selected from whole blood sample, red blood cell sample, buffy coat sample, plasma sample, serum sample, a sample from any other blood fraction, or any combination thereof.

The bodily sample may be from any living creature but preferably from warm blooded animals.

In some embodiments, the bodily sample is a sample from a mammal.

In some embodiments, the bodily sample is one taken from a human body.

In some other embodiments, the sample is taken from any domestic animal, zoo animals and farm animals, including but not limited to dogs, cats, horses, cows and sheep.

In some embodiments, the bodily sample may be taken from animals that act as disease vectors including deer or rats.

In some other embodiments, the sample is an environmental sample, such as, without being limited thereto water (e.g. groundwater) sample, surface swab, soil sample, air sample, or any combination thereof.

In some embodiments, the sample is a food sample, such as, without being limited thereto, meat sample, dairy sample, water sample, wash-liquid sample, beverage sample, and any combination thereof.

As a first stage in the method disclosed herein, the sample is stained with at least two dyes providing, under suitable conditions, two distinct stained areas in the sample.

A stained area may be defined, inter alia, with respect to, for example, background or collateral staining. For example, an intensity-based threshold, contrast-based threshold, edge detection, background subtraction, normalization, or combination thereof may be applied to define the stained area. Additionally, the definition of stained area may allow, inter alia, for diffuse boundaries, for example, by using a brightness-weighted sum/integral.

In some embodiments, such as in the case of membrane staining, a first stained area residing within a second stained area may be defined to include a case wherein the first area resides within the area circumscribed within the second area. For example, membrane staining of red blood cells may result in a second stained area that resembles narrow lines around the circumference of the cell (as viewed in a two-dimensional microscope image) in such a case, it may be determined that the first area resides within said second area if it falls within the stained cell circumference.

In some embodiments, standard microscopic sample preparation may be required for staining the sample. For example, sample preparation may take advantage of the well-known thin smear or thick smear method for blood smear preparation. As an alternative example, a drop of the sample is placed in the middle of a clean slide together with, before or after placing the dye and a cover slip is gently placed over the drop at an angle, with one edge touching the slide first. The liquid is then allowed to spread out between the two pieces of glass without applying pressure.

When referring to a dye it is to be understood as encompassing any chemical or biological substance that is capable of staining a component of a biological cell, to enhance contract and highlight structures of the stained object, be it a cell or part of a cell. The dye may have a class preference or specificity, e.g. may have preference or specificity to staining of nucleic acids and among the nucleic acid, to DNA or RNA, preference or specificity to amino acids, to lipids, carbohydrates etc.

When referring to preference or predominant staining it is to be understood that the dye stains one other cellular component in a particular color or fluorescence that is at least twice, three times, four times or even 10 times greater in its intensity than its staining intensity to another cellular component at that same color or fluorescence spectrum.

In some embodiments, when referring to preference or predominant staining it is to be understood that the dye has affinity (molecular attraction) to one cellular component (in the particular color or fluorescence spectrum) that is at least twice, three times, four times or even 10 times greater in its affinity to another cellular component (at that same color or fluorescence spectrum).

In some further embodiments, when referring to preference or predominant staining it is to be understood that the staining of DNA by the dye is stable or has more stability as compared to its staining of other components. Stability may be understood to mean that the staining produced by the dye remains substantially consistent for at least 30 minutes after being brought into contact with the dye, at times, at least 1 hour, 2 hours or even 5 hours after staining the sample with the dye having preference to DNA. Alternatively, stability may be understood to mean that the staining produced by the dye remains substantially consistent during exposure to light (e.g. light used for fluorescence excitation) for at least 0.25 seconds, 1 second, or even 15 seconds of exposure.

In this context, it is to be understood that the dye having preference to DNA may also stain other cellular components but with lower attraction or lower intensity or with a different florescence response (excitation spectrum anchor emission spectrum) such that it allows the greater enhancement of the DNA, which the dye has preference. For example, as will be further discussed below, under some conditions a dye may predominantly stain DNA, however, under some other conditions, the same dye may stain RNA.

Similarly, the staining of one other cellular component should be understood as encompassing staining of one or more cellular components other than DNA. This may also include staining of one or more cellular components in addition to DNA, but with no preference or lower preference to staining of DNA.

In some embodiments, the dyes are not cell type specific. In other words, the dye is not specific to a particular pathogen or to a particular stage of the life cycle of a particular pathogen or to a particular cell of the host being infected therewith and will stain a cell component irrespective of its origin, e.g. a DNA sequence or structure per se, an RNA sequence or structure per se, protein per se, etc.

The existence of a first stained area is determined based on various factors that may relate, inter alia, to the intensity of the stain, the shape of the stain, the variability or consistency of the stain etc. Once a first stained area is determined to exist, it is ascribed to the presence of DNA.

The method also provides a stained area of at least one other cell component being different from DNA. The stained area may be obtained from the same dye, under different conditions or by the use of a different dye.

Without being limited thereto, the at least one other cellular component is selected from the group consisting of RNA, proteins, lipids, membrane, cytoplasm, ribosomes, carbohydrates, glucans, glycoproteins, endoplasmatic reticuli, or any combination thereof.

In some embodiments, the at least one other cellular component is RNA.

There are a variety of dyes that may be used in accordance with the present disclosure. In some embodiments, the dye is a chromophore or fluorophore.

Dyes such as the Giemsa stain are known as chromogenic—their effect is to provide color or opacity to the sample and are visible, for example, in bright field microscopy.

In some embodiments, the dye provides fluorescent staining of the sample. Fluorescence is visualized by illuminating the sample with an “excitation” spectrum of light, which results in an “emission” at a distinct spectrum of light. Amongst the potential advantages of fluorescent stains is that the regions of the sample that are not stained show up as dark or nearly dark, thereby typically providing greater contrast between stained and unstained areas than chromogenic stains. Acridine Orange (AO) is an example of a dye used to fluorescent staining of biological samples.

In some embodiments, the dye is a cell permeating dye.

Without being limited thereto, a dye that predominantly stains DNA may be any member of the group consisting of acridine orange (AO, N,N,N′,N′-Tetramethylacridine-3,6-diamine, green staining), Hoechst family, DAPI (4′,6-diamidino-2-phenylindole), ethidium bromide (3,8-Diamino-5-ethyl-6-phenylphenanthridinium bromide), propidium iodide (2,7-Diamino-9-phenyl-10 (diethylaminopropyl)-phenanthridium iodide methiodide), SYBR family, YOYO, DRAQ family, SYTO family, TOTO family, or any combination thereof. Additionally the dye comprises a chemical modification of any of the aforementioned dyes that preserves its DNA preference.

Without being limited thereto, a dye that does not predominantly stain DNA may be any member of the group consisting of crystal violet (Tris(4-(dimethylamino)phenyl)methylium chloride), Hematoxylin stains, eosin stains, Safranin (azonium compounds of symmetrical 2,8-dimethyl-3,7-diamino-phenazine), acridine orange (AO, N,N,N′,N′-Tetramethylacridine-3,6-diamine, red staining), acid-Schiff stains, Masson's stain, Prussian blue, or any component or combination thereof. Many more stains that do not predominantly stain DNA are known in the art.

Dyes such as AO provide different fluorescence spectra for different cellular components. When AO stains DNA at neutral pH, it has an excitation maximum at 502 nm (cyan) and an emission maximum at 525 nm (green); when it stains RNA at neutral pH, the excitation maximum shifts to 460 nm (blue) and the emission maximum shifts to 650 nm (red). As such, it allows differential staining between DNA and RNA, depending on the excitation wavelength and conditions of the sample.

The Hoechst family of dyes are known by the chemical formula C₂₅H₂₆N₆R, with R representing a variety of possible substituents, such as, without being limited thereto, —OH (Hoechst 33258); —CH₂CH₃ (Hoechst 33342), —N(CH₃)₂ (Hoechst 34580), —SO₂NH₂ (Hoechst S769121).

In some embodiments, the method involves the combined staining with at least two dyes, the first dye being a member of the Hoechst family and the second dye being acridine orange.

When referring to a combination of two or more stains, it is to be appreciated that the two or more dyes may be added to the sample simultaneously or in sequence. Similarly, the respective stained areas may be obtained simultaneously or in sequence, as long as there is a time point that allows viewing two or more differently stained areas in the same sample.

In one embodiment, the method employs a combination of AO with the membrane-permeable dye that is essentially specific to nuclear DNA (e.g. Hoechst 33342, yielding a blue emission).

According to this embodiment, AO allows using the red-emission or a combination of the green and red emissions to stain the pathogen's cytoplasm (and possibly also the nucleus, but without substantially interfering with the Hoechst staining).

In some embodiments, the combination of AO and Hoechst allows the detection of a parasite. According to this embodiment and without being limited thereto, for the detection of a parasite, such as a member of the Plasmodium species, the concentration of Hoechst reagent such as Hoechst 33342 may be 10 μg/mL, but other possible values may be used as well, for example in the range between 3 μg/mL and 250 μg/mL; and AO may be used at 1.5 μg/mL, but other possible values may be used as well, for example in the range between 0.2 μg/mL and 125 μg/mL.

In some embodiments, the amount of AO and Hoechst reagent to be used is determined so as to provide, in the biological sample, a ratio therebetween. Accordingly, the Hoechst:AO ratio may be in the range of between 50:1 to 1:1, at times, about 7.5:1.

A same or similar ratio may also be applicable for other dye combinations, a first dye staining predominantly DNA and the other dye, one other component, as defined, namely, a ratio between the first dye and other dye in the range of between 50:1 to 1:1.

AO may additionally or alternatively be used to stain, for example, Plasmodium cytoplasm and/or food vacuole, but not the cytoplasm of the red blood cell (RBC) that the parasite may be inside, allowing the parasite's body to be seen without being obscured by an RBC even if present within the RBC.

Appropriate concentrations may be optimized with respect to factors such as the particular dye combination, desired duration of stain incubation, brightness of resulting color or fluorescence, and character of the resulting staining.

In some embodiments, the method disclosed herein is applicable for the detection of an infection by a DNA-carrying pathogen. As such, at least the first dye stains at least the DNA, if present in the sample to thereby provide a first stained area indicative of the presence of the DNA carrying pathogen in the sample.

The pathogen may be any infectious microorganism. An some embodiments, the pathogen is a eukaryotic parasite. When referring to eukaryotic parasite, in the context of the present disclosure, it is to be understood as encompassing one cell parasites and multicellular parasites but also fungi, such as yeast (e.g. Candida) and Aspergillus.

In some embodiments, the pathogens are bacteria. This includes, for example and without being limited thereto, Escherichia coil, Staphylococcus aureus, Microbacterium tuberculosis, Salmonella species, Borrelia species and Treponema pallidum and others known.

In some embodiments, the pathogen is a eukaryotic parasite. In accordance with this embodiment, the parasite may be a one cell parasite, such as protozoa. This includes genital protozoa, e.g. Trichomonas vaginalis, nervous system protozoa, e.g. Naegleria fowleri fecal protozoa, e.g. Giardia lamblia, blood protozoa. In some embodiments, the pathogen may be a multicellular parasite, such as Wuchereria bancroft, Brugia malayi, Brugia timori, Mansonella streptocerca, or Onchocerca volvulus.

In some embodiments, the parasite is a blood protozoa selected from the genuses consisting of Trypanosoma (causing Chagas disease and African sleeping sickness), Plasmodium (causing Malaria); Toxoplasma (causing Toxoplasmosis); Babesia (causing Babesiosis).

Specifically, when referring to Plasmodium it is to be understood as encompassing at least any member of the group consisting of Plasmodium falciparum (P. falciparum), Plasmodium vivax (P. vivax), Plasmodium ovale (P. ovale), Plasmodium malariae (P. malariae), and Plasmodium knowlesi (P. knowlesi).

In some embodiments, pathogen is understood to mean a particular stage of the life cycle of a particular pathogen or group thereof. For example, the invention disclosed herein can be applied specifically to the detection of trophozoites, schizonts or gametocytes of Plasmodium species or P. falciparum in particular.

As may be appreciated, the method disclosed herein may be applicable for the detection of multiple pathogens using the same conditions and/or in the same sample, e.g. same combination of dyes, same test conditions etc., as well as for the detection of a pathogen at multiple stages of its life cycle. In some embodiments, the method disclosed herein may determine which one or more of the multiple pathogens (or life stages) is suspected.

In some embodiments, the method disclosed herein is for detecting Plasmodium infection in a human blood sample, the method comprising:

-   -   staining the human blood sample with at least two dyes, under         conditions that allow at least staining of DNA and at least one         other cellular component being different from DNA;     -   identifying at least a first stained area comprising the DNA, if         exists in the blood sample, and at least one other stained area         comprising one other cellular component in the blood sample;     -   extracting structural features for the first stained area and         the at least one other stained area, said spatial features         comprising size of at least one of the first stained area and         one other stained area and a location of the first stained area         and the at least one other stained area one with respect to the         other;     -   determining value or combination of values being indicative of         the presence of suspected Plasmodium in the blood if a first         stained area was identified and said structural features fall         within limitations predetermined as characterizing a pathogen         infection.

In some embodiments relating to determination of the presence of Plasmodium in the blood, the stained object is obtained by staining the blood sample with a combination of acridine orange (AO) and Hoechst dye, in particular, Hoechst 33342 with a concentration ratio between AO and Hoechst 33342 in the range of 1:50 and 1:1, at times, even in the range of 1:7.5.

In accordance with the above embodiment, the method is applicable for detection of malaria infection in a human blood sample.

Once the sample is stained with the one or more dyes, at least one stained object is obtained and the method then involves selecting at least one stained object in the sample and obtaining structural or spatial features of the stained object.

When referring to spatial or structural features of a stained object it is to be understood as encompassing any measurable feature of the stained areas in the selected stained object. The features may be presented as a discrete value or as a range of values characterizing the stained area.

In some embodiments, the structural features include at least one of the size (e.g. dimension, length, circumference, minimum width, maximum width, or area) of the stained areas and/or the location of the first stained area with respect to the location of the other stained area or areas. In other words, the method may be performed based at least one either determining dimensions, e.g. area of the stained areas, or on the location of the first stained area with respect to the location of the other stained area or areas. These features may be combined also with one or more additional features.

The additional structural features may include, without being limited thereto, shape of stained area(s), pattern of movement of stained area(s), intensity of stained area(s), color of stained area, texture (contour) of stained area, sharpness of boundary of stained area, pattern of staining in intensity or color, overlap of stained area with other stained areas or image features, relative size of stained area to other stained areas or image features, proximity or contact of stained are to other stained areas or image features.

In some embodiments, the bodily sample is a blood sample.

In some embodiments, the pathogen is a blood parasite.

In some embodiments, the bodily sample is human blood and the pathogen is Plasmodium species responsible for human malaria, such as those selected from the group consisting of P. falciparum, P. vivax, P. ovale and P. malariae.

When the bodily sample is a blood sample, the extraction of structural features comprises selecting a stained object in the blood sample that comprises the first stained area and the at least one other stained area.

Based on the stained areas and the analysis of the structural features a high probability of the sample being infected with a suspected pathogen is determined. Thus, in the context of the present disclosure, when referring to determination of presence of a pathogen or suspected pathogen it is to be understood that any one of the following is determined:

-   -   that one or more suspected pathogen are present in the sample;     -   that one or more suspected pathogens are present in the sample         at a confidence levels above a predefined threshold; the         confidence levels may increase or a final determination of the         presence of a suspected pathogen may require one or more         additional analysis steps.     -   that one or more suspected pathogens may be present in the         sample with a determined or estimated confidence scores or         probabilities that are available for additional analysis steps

In accordance with some embodiments, a suspected pathogen is determined to be present in the sample if a first stained area is identified (being indicative of the presence of DNA in the sample), and the first stained area abuts with, is in close proximity to, or resides within the one other stained area and the size of at least one of the first stain, i.e. the DNA containing area, and of the one other stain is within a predetermined range. For example, a DNA containing area often lies near an area stained for RNA, which exists in the cytoplasm.

In accordance with some other embodiments the suspected pathogen is determined to be present in the sample if a first stained area is identified (again, being indicative of the presence of DNA in the sample) and the size of the first stained area satisfies a predetermined relation with respect to the size of the one stained area. This criterion can be used, for example, to differentiate targeted eukaryotic parasites from bacteria: in eukaryotic cells, the area predominantly stained for DNA should be smaller than a cytoplasmic staining, indicating a distinct nucleus that is not present in bacteria.

In accordance with yet some embodiments, the presence of a suspected pathogen is determined if a first stained area is identified and the dimensions or area of the first stained area is within a range of values predetermined to be associated with the particular pathogen or with a particular stage of the life cycle of a particular pathogen. For example, if the pathogen is one causing malaria (i.e. Plasmodium), the area of the first stained area would typically not be below 0.2 μm² or above 20 μm² or would be in the range of 0.2 μm² to 20 μm². In some embodiments, the area of the first stained area in detection of Plasmodium would not be below 0.8 μm² or above 13 μm² or would be within the range of 0.8 μm² to 1.3 μm².

In accordance with some other embodiments the presence of a suspected pathogen is determined to be in the sample if a first stained area is identified and the areas of the one other stained area are within a range of values predetermined to be associated with the particular pathogen or a particular stage of the life cycle of a particular pathogen. For example, if the pathogen is one causing malaria (i.e. Plasmodium), the area, for example, a cytoplasm, of the other stained area would typically not be below 0.8 μm² or above 65 μm² or would be in the range of 0.8 μm² to 65 μm². In some embodiments for detecting malaria infection, the area of the other stained area is not below 1.6 μm² or does not exceed 40 μm² or is in the range of 1.6 μm² to 40 μm².

Considering the above features, it is understood that in accordance with some embodiments of the present disclosure, particular area of the first stained area cannot exceed particular area of the one other stained area. Similarly, the dimensions of the first stained area should be statistically significant (e.g. by t-test) smaller than the dimensions of the other stained area.

In some other embodiments, the presence of a suspected pathogen is determined to be in the sample if a first stained area is identified and the first stained area occupies a predetermined % volume of the all other stained areas. For example, when referring to malaria, the first stained area would typically occupy between 12% to 60% of said one other stained area.

In accordance with some other embodiments the presence of a suspected pathogen is determined to be in the sample if a first stained area is identified and the first stained area and the one other stained area have predetermined shapes. For example, the trypomastigote stage of Trypanosoma brucei is known to have an elongated, rod like shape. Other shapes may include, without being limited thereto, spiral, oval, elongated and spherical properties.

In accordance with some embodiments, the presence of a suspected pathogen is determined to be in the sample if a first stained area is identified and the first stained area has a variability in intensities that is above a predetermined threshold. The variability of intensities may appear as a cluster of more than one area stained with the first stain (plurality of first stained area) or as an irregular shaped first stained area having different shades of color or fluorescence. This may reflect, for example, a multinucleate stage in the development of a protozoan, such as schizonts of Plasmodium.

Yet further, in accordance with some embodiments the presence of a suspected pathogen is determined if a first stained area is identified and the pattern of movement directionality and/or velocity) of the stained object corresponds with a pattern predetermined to be associates with the suspected pathogen. For example, when considering Trypanosoma brucei, its motion (motility) is expected to occur at a characteristic pattern. As such, when the sample is stained with AO and Hoechst staining, the movement of the AO stained area may be analyzed to confirm a match or an expected correlation with the expected pattern.

In yet some other embodiments, the presence of a suspected pathogen is determined if during movement of the stained object the first stained area is maintained within boundaries of the one other stained area. Thus, when referring to the above example with Trypanosoma brucei, the movement of the Hoechst stained area may be analyzed to ensure that a putative nucleus remains at all times within the moving AO stained area.

The structural features may be determined by simple viewing the sample, however, in some embodiments they are preferably determined based on one or more optical images of the sample. Thus, in accordance with some embodiments, the method comprises capturing at least one optical image of the stained object and extracting the structural features from the at least one optical image.

At times, particularly when the structural parameter includes motion or movement of the stained object, more than one optical image is captured and the structural parameter of motion is determined based on a sequence of images in time.

Needless that state, the more accumulated (or collected) information of structural parameter(s) of the stained object, the more accurate the determination and identification of a pathogen in the sample may be.

The structural features may be analyzed manually, or by the use of a dedicated system for allowing an automated and as such, relatively fast detection and/or identification of the pathogen in the bodily sample. The result of the analysis may retrieve a Yes/No indication of the presence of a pathogen, a probabilistic indication of the presence of a pathogen, images of a suspected pathogen for further analysis (manual or automatic) and/or may provide a more specific result, including the type of the pathogen, level of invention (count/μl) etc.

The use of an automated system may be of significance, not only for overcoming human errors in analyzing the stained objects in the sample and saving time and labor, but also since certain components of a bodily sample may not stain immediately and/or the degree of staining may vary significantly over time, as is the case in sometimes with Hoechst 33342 staining of blood contaminated cells. Consequently, image characteristics may vary depending on how quickly the sample is analyzed. As such, there is an advantage of having an automated system allowing the rapid, or even almost instantaneous, imaging and analysis of the stained sample.

Thus, in accordance with a further aspect of the present disclosure there is provided a system comprising:

-   -   an image capturing component configured and operable to capture         at least one optical image of a stained area in a sample, the         stained area comprising a first stained area corresponding         predominantly to DNA and at least one other stained area         corresponding to at least one other cellular component being         different from DNA;     -   an image processing unit configured to extract structural         features of said at least first stained area and said one other         stained area, said structural features comprising at least size         of at least one of said first stained area, and one other         stained area; and a location of the first stained area and said         one other stained area one with respect to the other; and         determine that a pathogen is present in the sample, if a first         stained area is identified and the structural features conform         to structural features predetermined as characterizing a         pathogen infection.

In some embodiments, the system also includes an output unit for providing an output comprising a value or combination of values being indicative of the presence or absence of suspected pathogens in the sample.

In some embodiments, the system is preferably computer-based using a collection of parameters being stored therein and corresponding to, inter alia, structural features associated with at least one defined pathogen: The parameters may, for example, include expected values or ranges of values of the structural features, associated with a pathogen, or parameters that control the execution of machine-learning or data analysis algorithms. The parameters may be derived from information gathered a priori or simultaneously obtained based on reference samples including pre-determined pathogens.

The parameters may also comprise information relating to the behavior of a pathogen, or cell infected with a pathogen, such as motility and variations in features depending on the particular stage of the life cycle of a particular pathogen.

The parameters may also comprise information regarding conditions to be used for the detection of a pathogen on a type of bodily sample, e.g. on blood sample, statistical information regarding the staining qualities and variability of a set of dyes to be used for a particular bodily fluid, alternative dye combinations or condition combinations, etc.

In some embodiments, the collection of stored parameters comprises parameters associated with a plurality of pathogens. In some embodiments, the collection of stored parameters comprises parameters that associated with determining which one or more pathogens is suspected.

In some embodiments, the collection of parameters is associated with blood borne pathogens. In some other embodiments, the collection of parameters is associated with blood parasites. In some particular embodiments, the collection of parameters is associated with pathogens that harbor the human blood, in particular, of a Plasmodium species responsible for human malaria, such as those selected from the group consisting of P. falciparum, P. vivax, P. ovate and P. malariae.

Further provided by the present disclosure is an image processing unit for identifying a pathogen in a sample, comprising:

-   -   input module configured and operable to receive (image) data         corresponding to the stained object in the sample comprising at         least a first stained area corresponding predominantly to DNA         and at least one other stained area corresponding to at least         one other cellular component different from DNA, and     -   an image processing unit configured and operable to process the         data corresponding to the stained object, the processing         comprises:         -   extracting structural features for the at least the first             stained area and the one other stained area in the stained             object, said structural features comprising at least one             of (i) size of at least one of the first and the one other             stained areas and (ii) location of said first stained area             and said one other stained area one with respect to the             other; and         -   providing a value or combination of values being indicative             of the presence or absence of a pathogen in the sample, if             said structural features conform to structural features             predetermined as characterizing a suspected pathogen.

Several modes of operation may be used with respect to the system and image processing unit, Automated as well as manual and semi-automated systems can be employed.

With respect to the system, the image capturing component may be any device configured and operable to acquire at least one optical image of the stained object being selected, for example, a CCD or CMOS camera. The image capturing component may be equipped with conventional functionalities, such as focus functionalities. The image capturing component may also include lenses, aperture and shutter.

The image capturing component provides image data for processing by the image processing unit. The image data in the context of image analysis is based on a collection of pixel information that essentially covers one or more Regions of Interest (ROI).

The image data typically including the pixel information may be presented in any available format, including, without being limited thereto, Tagged Image File Format (TIFF), Joint Photographic Experts Group (JPEG), Graphic Image Format (GIF), Portable Network Graphics (PNG), Portable Document Format (PDF), bitmap (BMP), and raw image-sensor data. Image data can be in a compressed data format or in an uncompressed data format; may relate to any gray or color scale; can include bitmap data, or a portion of a bitmap file containing bitmap data.

Once one or more images are captured, they are processed by the image processing unit. The processing by the processing unit is configured and operable to provide one or more values of structural features of the stained areas. In other words, based on image analysis techniques, various output values relating to structural features of the stained areas are determined, which may allow the identification of the presence or absence of the suspected pathogen in the sample or estimation of the probability of presence therein. The values may include the dimensions of one or more other stained areas in the ROI, the relationship between the stained areas, and/or averages, compounding or statistics of values pertaining to structural features. The processing may include, in some embodiments, analyzing the one or more values or combination of values corresponding to structural features with respect to the parameters e.g. values or ranges of values or appropriate machine-learning weights) that have been a priori determined for characterizing one or more pathogens, or differences therebetween.

The image analysis can be based on one or more of the common practices such as contour detection, image parameter derivatives, shape detection, image reconstruction, segmentation, image differencing, pattern matching, matched filtering, machine learning and geometric hashing.

Data processing by the image processing unit may use a classification module. The classification module can be provided with at least one structural parameter previously determined for a pathogen. The classification module can analyze the structural features provided and deduce a selection of possible pathogens being identified. By way of an illustration, a classifier can identify a plurality of possible pathogens or a single type of pathogen.

In particular embodiments, the structural features determined are associated to an expected pathogen and these are analyzed with respect to the pre-defined parameters.

It should be noted that the identification of a single pathogen may be a complex process which includes different combinations of features. Therefore, structural features determined following the use of a particular combination of dyes can be used as criteria for subsequent analysis of a further combination of dyes. For example, structural features identified in a previous analysis can be used to continue the identification process while focusing of a subset of possible combination of dyes. For example, in a biological family level of identification of a pathogen, the results of previous analysis may provide a list of possible best filter(s) selection to be used in a next round of analysis.

In some embodiments, image analysis and determination of the presence of suspected pathogens or a value or values indicative with the presence of suspected pathogens can take advantage of one or more machine-learning algorithms, which operate on a plurality of structural features or related values. Such algorithms include without limitation Support Vector Machines (SVM), Artificial neural networks, Naive Bayes classifiers, Bayesian networks, Decision trees, Nearest Neighbor Algorithms, Random Forests, Boosting, Regression analysis, Linear classifiers, Quadratic classifiers, k-nearest neighbor, Hidden Markov models and any combination thereof. The result of the one or more machine-learning algorithms can comprise one or more confidence score, probabilities and/or yes/no decisions.

As appreciated, the more features determined in the analysis—the more precise is the identification process. By using a plurality of dyes to induce a plurality of structural features, the risk for misdetection or misclassification is reduced. However, added features may also correspond to increased computational or operational load. Some embodiments strive to balance the added benefit of added features with the associate load drawbacks.

Based on the value or combination of values obtained by the analysis, various decisions are made by the processing unit as to the presence or absence of a pathogen in the sample, including, at times, the type of the pathogen (qualitative identification) and/or the amount (quantitative identification) of the pathogen in the sample.

The processing unit is also configured to communicate with an output unit. Thus, based on the output value or values of the structural features determined by the processing unit, an output signal or output signals indicative of presence or absence of at least one pathogen and in some embodiments, the type of the pathogen, in the acquired image is provided by an output unit.

The output may be provided in any acceptable form, including a graph, graphic or text displayed on a monitor of a control unit, a printout, as a voice message, or a user's smartphone display, for accepting processed data from the processing utility and displaying information relating to the structural features obtained and/or associated values determining the presence and optionally the identity of a pathogenic infection, using, lists, tables, graphs etc. A monitor may be connected to a printer for printing the output.

The processing unit may also include a user interface module, e.g. a keyboard, or a touch screen for allowing a practitioner, performing the method of some embodiments of the invention, to control the operation of the system, including, inter alia, input data with respect to the examined bodily fluid source, date, place, etc.) conditions of operating the system, types of dyes used, number of images to be taken, time interval between images, etc.

At times, image analysis may also involve adjustment or normalization of image brightness on the basis of degree of staining of the sample. These may be based on, for example, identifying one or more of brightest and/or dimmest pixel values in the image or set of image (for example, corresponding to a particular sample), average brightness of brightest and/or dimmest area, and/or image histogram. Such features may be extracted from a representative image (not necessarily the one being normalized) from statistical analysis of multiple images. The features used for normalization may be based on a single or multiple images, which may be captured using different excitation wavelengths (as in AO providing different colors under different illumination wavelengths).

Image brightness may also be adjusted using other control means, such as image capturing component exposure time and/or brightness of illumination.

Further, the conditions of operating the system may allow timing of the image acquisition, e.g. to allow sufficient incubation time with the one or more dyes as well as the operation with different optical configurations of excitation and/or emission wavelengths, in order to image the stained sample at various colors or fluorescence spectra.

In order to image the stained sample at various colors or fluorescence spectra, changes in excitation may be achieved by switching the color of illumination. This can be done, for example, by providing two or more light sources (e.g. for AO, UV LED light at 365 nm and blue LED light at 475 nm) and combining them optically (for example, using a dichroic mirror or grating).

In another example, a single illumination source (e.g. UV LED light at 365 nm) may be used to excite two dyes simultaneously, and one or more optical filters are moved in or out of the optical path to select the relevant emission wavelengths. Other dye sets can be simultaneously excited using the same incident illumination as described here, even if one or more of the dye is excited non-optimally. As an example, AO can be similarly co-excited together with a Hoechst stain, DAPI and DRAQ stains.

In yet another example, a single illumination source (e.g. LTV LED light at 365 nm) may be used to excite two or more dyes simultaneously, and the emission optical path is split such that the two or more emissions are captured on two or more image capturing components.

In yet another example, a color imaging sensor is used to simultaneously capture two or more fluoresce signals. Use of a color imaging sensor can, for example, obviate the need for one or more optical filters that are moved in or out of the optical path to select the relevant wavelength.

In the context of the present disclosure various illumination sources may be used, these include, without being limited thereto, those providing white light (as in bright light microscopy), UV light, blue light, green light, yellow light, red light, combination thereof, or any light applicable for exciting one or more of the dyes used for staining.

The components of the system, namely, the image capturing component, the processing unit, the output unit etc. may be directly connected to each other (e.g. directly by a wire) or one or more of the components may be remote from one or more other components. For example, the image capturing device may send data to a processing unit over an intranet or over the Internet, to allow processing at a remote location.

An example of a system which may be used for performing the method of the present disclosure is described in PCT patent application publication No. WO 2012/090198, the content of which is incorporated herein, in its entirety, by reference.

The processing unit is typically operable by running a dedicated program of instructions (e.g. software application) that performs the analysis and storage of incoming data. The software application may be embodied in a program storage device readable by machine, such as a CD or memory disk.

In line with the above, the present invention also provides a program storage device readable by machine, tangibly embodying the program of instructions executable by the machine to perform the method disclosed herein, namely, a method of detecting a pathogen infection in a sample, the method comprising:

-   -   staining said fluid sample with two or more dyes, said two or         more dyes providing differential staining of at least DNA and at         least one other cellular component being different from DNA;     -   identifying at least a first stained area corresponding         predominantly to DNA and at least one other stained area         corresponding to the at least one other cellular component;     -   extracting structural features for the at least a first stained         area and the one other stain area, said structural features         comprising at least size of at least one of the first and one         other stained areas and a location of said first stained area         and said one other stained area one with respect to the other;     -   determining a value or combination of values being indicative of         the presence of a pathogen in the sample if said structural         features correspond to structural features predetermined as         characterizing a pathogen infection.

Yet further, the present disclosure provides a computer program product comprising a computer useable medium having computer readable program code embodied therein for detecting a pathogen infection in a bodily sample bodily sample being stained with two or more dyes, the computer program product comprising:

-   -   computer readable program code for causing the computer to         identify in a stained object within the bodily sample;     -   computer readable program code for causing the computer to         identify in the stained object at least a first stained area         corresponding predominantly to DNA and at least one other         stained area corresponding to at least one other cellular         component being different from DNA;     -   computer readable program code for causing the computer to         extract structural features for the at least a first stained         area and one other stain area, said structural features         comprising at least size of at least one of the first and one         other stained areas and a location of said first stained area         and said one other stained area one with respect to the other;     -   computer readable program code for causing the computer to         determine a value or combination of values being indicative of         the presence of a suspected pathogen in the sample if said         structural features correspond to structural features         predetermined as characterizing a pathogen infection.

Finally, the present disclosure provides a kit comprising:

-   -   a first dye predominantly staining DNA;     -   a second dye for staining at least one other c component being         different from DNA;     -   instructions for use of said first dye and second dye for         determining presence of a suspected pathogen in a bodily sample.

In accordance with this aspect, the first and second dye may be provided in a single composition or in a first composition comprising the first dye and a second composition comprising the second dye. The first and second composition each comprising, in addition to the dye, a carrier suitable for use in staining the bodily sample with the respective dyes.

The kit disclosed herein is to be used for performing each of the steps and conditions of the method disclosed herein.

In some embodiments, the first dye comprises a Hoechst dye. In some embodiments, the second dye comprises acridine orange.

In some embodiments, the kit comprises instructions for providing the bodily sample with the first dye and the second dye at a ratio the range of between 50:1 to 1:1.

In some embodiments, the first dye comprises Hoechst dye, specifically Hoechst 33342 and the second dye comprises AO, the concentration of the first dye is in the range between 3 μg/mL and 250 μg/mL; and the concentration of AO is in the range between 0.2 μg/mL and 125 μg/mL.

In some other embodiments, the first dye comprises Hoechst dye, specifically Hoechst 33342 and the second dye comprises AO, the concentration of the Hoechst 33342 is about 10 μg/mL and the concentration of AO is about 1.5 μg/mL.

In some embodiments, the first and second dyes may be combined with a suitable buffer, such as, without being limited thereto one comprising 1% Tris-EDTA buffer, 4.5% DDW and 92.5% saline.

Without wishing to be bound by theory, it is possible that the AO/Hoechst staining provided more robust and stable staining which enabled rapid and efficient machine vision of the dyed sample. This allowed imaging of a greater amount of blood than may be examined under a microscope in conventional methods, which in turn provided higher sensitivity at low parasitemia. It is also possible (in addition or alternatively) that one or more of the applied criteria of analysis provided dependable results that are not dependent on the human factor

Some embodiments of the present disclosure will now be exemplified in the following description of non-limiting examples that were carried out in accordance with the disclosed method. It is to be understood that these examples are intended to be in the nature of illustration rather than of limitation. Obviously, many modifications and variations of these examples are possible in light of the above teaching. It is therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise, in a myriad of possible ways, than as specifically described hereinbelow.

DESCRIPTION OF SOME NON-LIMITING EXAMPLES

Detection of Plasmodium in a Blood Sample

A blood sample obtained from a human subject being identified as having malaria infection was stained with a dye solution comprising 2 μg/ml Acridine Orange, 15 μg/ml Hoechst 33342, 1% Tris-EDTA buffer, 4.5% DDW and 92.5% saline.

After staining, the samples were imaged using different color of illumination, using UV LED light at 365 nm to image AO staining and blue LED light at 475 nm, to image the Hoechst staining). The sample was also imaged in the bright field (illuminating with white light).

The resulting images are provided in FIG. 1A-1F, with FIGS. 1A-1C being obtained from a sample of white blood cells, and FIGS. 1D-1F being obtained from the malaria infected red blood sample.

Specifically, FIG. 1A shows in the bright light field image, which shows the boundaries (the membrane shown by the arrow in FIG. 1A) of a white cell and that the DNA staining area (arrow in FIG. 1B) and of the other component stained area (in this case the cytoplasm shown by the arrow in FIG. 1C) have dimensions that are typical to a white blood cell (both DNA and RNA staining being larger than typical for a Plasmodium parasite).

However, FIGS. 1D-1F show that first stained area (DNA, shown by the arrow FIG. 1E) and the second stained area (RNA, white spot in FIG. 1F) are much smaller than the boundaries of the cell (as shown by the arrow in FIG. 1D), being indicative of an infection of the anucleated red blood cell.

Notably, in a non-infected sample, no stained areas corresponding to those shown in FIG. 1E and FIG. 1F are obtained.

These results show that by staining with at least two dyes, one predominantly staining DNA (in this particular case Hoechst 33342) it is possible to identify Plasmodium infection in a red blood cell.

Level of Confidence of Detection

In this study, a group of 200 blood samples was tested in accordance with an embodiment of the present disclosure. Of these blood samples 100 were determined to be positive for malaria using Giemsa stain based on standard microscope methodology and 100 being determined to be negative. A duplicate of each of the 200 samples was stained with a dye solution to have a final concentration in the tested sample of 2 μg/ml Acridine Orange and 15 μg/ml Hoechst 33342 and then analyzed using automated machine vision under bright field, UV light and blue light, essentially as described above. The results showed that more than 97% of the samples that were identified as infected under the conventional method were also identified as such using the AO/Hoechst stain. Out of the 100 samples that were deemed healthy using the conventional Giemsa stain, 93 were confirmed using the AO/Hoechst stain, but seven samples were identified as infected. These seven were then once again analyzed using Giemsa reagent (either by repeating both staining and microscopy with a new sample from the same donor or by further microscopy of the original preparation which gave rise to the negative result). In all seven cases it was confirmed that indeed they were infected, but apparently at a low parasitemia of under 1,000 parasites/μl.

The above shows that not only the method disclosed herein allows detection even by machine vision) of infection with high level of confidence (above 97%), but also when parasite count is very low (low parasitemia), even under 1,000 parasites per μl, or under 500 parasites per μl and even at 20 parasites/μl. 

The invention claimed is:
 1. A method for identifying a white blood cell within a blood sample, the method comprising: staining the blood sample with at least a first dye that predominantly stains DNA, and a second dye that stains at least one other cellular component being different from DNA; using a microscope, acquiring a plurality of images of the blood sample, at least one first one of the images being acquired while the blood sample is illuminated under brightfield conditions, at least one second one of the images being acquired while the blood sample is illuminated by a light source having an illumination wavelength that causes the first dye to fluoresce, and at least one third one of the images being acquired while the blood sample is illuminated by a light source having an illumination wavelength that causes the second dye to fluoresce; and using at least one computer processor, identifying the white blood cell within the blood sample, by: identifying an object within the plurality of images as being a white blood cell candidate, by analyzing the first one of the images; identifying that a first stained area, which is stained by the first dye, is disposed within the white blood cell candidate, by analyzing the second one of the images; identifying that a second stained area, which is stained by the second dye, is disposed within the white blood cell candidate, by analyzing the third one of the images; and determining that one or more structural features of the first and second stained areas satisfy predetermined criteria associated with a white blood cell, the structural features comprising the sizes of the first and second stained area relative to a size of the identified object.
 2. The method according to claim 1, wherein identifying the white blood cell comprises distinguishing between the white blood cell and a pathogen.
 3. The method according to claim 1, wherein identifying the white blood cell comprises determining that sizes of the first and second stained areas are similar to that of the identified object.
 4. The method according to claim 1, wherein identifying the white blood cell comprises determining that sizes of the first and second stained areas are not substantially smaller than that of the identified object.
 5. The method according to claim 1, wherein staining the blood sample with the second dye comprises staining the blood sample with Acridine Orange. 